Sparkover control circuit for lightning arrester shunt gap unit



@et l?, H9? J. s. KRESGE 39343710@ SPRKOVER CONTROL CIRCUIT FORLIGHTNING ARRESTER SHUNT GAP UNIT Filed March 22, 1965 y G51 5,4 R4 Q4United States Patent O 3,348,1@ SPARKVER 'CONTROL CHRCUH' FOR LIGHT-NlNG ARRESTER SHUNT GAP 'UNIT .lames S. Kresge, Pittstield, Mass.,assignor to General Electric Company, a corporation ot New York lFiiedMar. 22, i965, Ser. No. 441,632 Claims. (Cl. 317-70) ABSTRACT 0F THEDISCLSURE A sparkover controlling network comprising auxiliary gaps,impedances and preionizers for a current switching main multi-gap whichshunts extra series valve resistance in a valve type lightning arrester.

This invention relates to lightning arrestors and more particularly toimprovements in current switching shunt gap units for valve typelightning arrestors for use 0n high switching surge energy systems suchas extra high voltage transmission lines and lower voltage cablecircuits.

Alightning arrestor is an electrical analog of a mechanical safety valvein that it prevents the escape of normal electrical pressure (voltage)while automatically permitting the escape or release of excess pressureso as to prevent rupture of the electrical pressure containing means(insulation) of electrical apparatus such as power transmission ordistribution circuits yof either the open air line type or the cabletype. As indicated by the name lightning arrester, lightning is thehistorical cause of such excess voltage although switching surges havelong been recognized as another cause.

As power system operating voltages have increased progressively throughthe years to 230 kv., then to 340 kv., and now through 500 kv. to 700kv., it has been found that the still more rapid accompanying increasein switching surge energy (the latter being proportional to the productof the system capacitance and the square of the system operatingvoltage) imposes a higher duty on the arrestor than lightning surges.One way to enable an arrestor to discharge the very high switching surgeenergy lof 500 kv. and 700 kv. systems is to provide it with additionalvalve resistance material shunted by a current switching gap unit whichin general is only sparked over by lightning surges but on occasion mayalso be sparked over during discharge of lower voltage magnitude, butlonger duration, switching surges. In a time which is long compared withthe duration of a typical lightning surge but short compared with theduration of a typical switching surge, the shunt gap, if it has becomesparked over, develops enough arc voltage to switch practically all thearrester current into the additional valve resistance material so thatthe latter is not only always available to absorb switching surge energyfor practically the entire duration of a switching surge, but it is alsoalways available to limit power frequency current following a lightningsurge.

ln order to develop suiciently high arc voltage, it is necessary greatlyto elongate the arc and in shunt current switching gap units this isachieved in a reasonable space by having each unit consist of amultiplicity of similar spark gaps connected in series with each otherand with a magnetic Coil for providing a common magnetic field forelongating the individual arcs, the sum of whose lengths is the totalarc length of the unit. Usually the coil is Vprotected againstover-voltage by a shunt gap generally similar to the other gaps fordeveloping an arc voltage for rapidly switching the arrester currentinto the coil.

A problem with such shunt current switching gap units is to give them asufficiently low sparkover voltage and Bdld@ Patented Get. l?, 1967 ICCmake that sparkover voltage highly stable and independent of the waveshape of the applied voltage.

The current switching shunt gap should have a low enough sparkovervoltage setting so that on lightning surges it always sparks over at alow enough voltage to prevent the extra resistance in the arresters fromincreasing the arrester voltage above the maximum of what it would be ifthe extra resistance were not present. On the lother hand, the currentswitching gap should have a high enough sparkover setting so that itshigh arc voltage will not cause restriking on power follow currents andswitching surges. Ordinarily with a plurality of similar spark gapsconnected in series, the sparkover voltage of the series circuit isapproximately equal to the number of gaps multiplied by each onesindividual sparkover voltage. It is, of course, impossible to make thesparkover voltage of the series circuit or combination less than thesparkover voltage of each of its components. Being shunted by a resistorin series with a main gap or gaps, the shunt gap does not have towithstand the system operating voltage and hence can have a sparkovervoltage which is independent of system voltage. Anomalous as it mayseen, such gap units can have a higher arc voltagethan sparkover voltagebecause the arc voltage is the sum of the are voltages of the individualserially connected gaps. In the case of a single gap, this would be animpossible contradiction of terms because there can be no single arcwhose counter voltage exceeds the voltage creating it.

Accordingly, it is an object of the invention to provide a new andimproved sparkover control circuit for lightning arrester gap units.

It is another object of the invention to provide a new and improvedsparkover control circuit for lowering the sparkover voltage of amultiple gap unit to a desired value anywhere between the sparkovervoltage of one gap of the unit and the sum of all of the gaps of theunit.

It is a further object of the invention to provide a sparkover controlcircuit for current switching gap units 'which is substantiallyindependent of wave shape of the applied voltage.

It is an additional object of the invention to provide a new andimproved sparkover control circuit in which certain elements provide thedual function of preioning associated main gaps and also controlling thesparkover voltage distribution between the main gaps so as to providecascading sparkover of the individual gaps.

Briefly described, the invention utilizes a novel auxiliary networkwhich applies a greater than pro rata proportion of the applied voltageto an individual main gap until it sparks over, after which itprogressively applies nearly the full applied voltage to the remainingmain gaps sequentially so as to cause them to break down or spark oversequentially in a cascading manner. The invention also includes simplemeans for adjusting the voltage at which the ysparkover sequencecommences and further provide-s separate means for compensating thecircuit for the effect of changes in wave shape of the applied voltage.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

In the drawing,

FIG. 1 is a block diagram of a lightning arrester in which the inventionis adapted to be used,

FIG. 2 is a circuit diagram of an embodiment of the invention, and

FIG. 3 is a circuit diagram of a modification thereof.

Referring now to the drawing and more particularly to FIG. l, there isshown therein a module 1 of a lightning arrester adapted for use onextra high voltage circuits such as circuits of 500 kv. or 700 kv., itbeing understood that in practice such a lightning arrester wouldconsist of a large number of such modules connected in series. Themodule l consists of a main series gap unit 2 which may either be of thecurrent limiting or the noncurrent limiting type, the former being onewhich develops an arc voltage soon after sparkover comparable to itssparkover voltage and the latter being an ordinary current interruptingor are quenching gap unit which does not develop substantial arc voltagebut rapidly develops recovery voltage after normal current zero.Connected in series with the main gap unit is a main series valveresistor 3 ordinarily of well-known material having a negativeresistance characteristic. Also connected in series with the arrester isan additional shunted valve resistor 4 generally similar to 3 which isshunted by a shunt gap unit 5 of the current switching type whichrapidly develops an arc voltage after spark over comparable to itssparkover voltage so as to switch the arrester current into theadditional valve resistor material, the function of such additionalresistor material being to absorb switching surge energy and limit powerfollow current.

Inasrnuch as the shunt gap unit 5 does not have to withstand appliedpower frequency voltage, it does not have to have as high a sparkoverlevel as the main series gap unit 2, and in fact it is necessary that ithave a comparatively low sparkover voltage level so as to take theadditional valve resistor material out of the circuit to limit thedischarge voltage of the arrester to the desired protective levels whiledischarging lightning surges. l

Referring now to FIG. 2, which shows a circuit of a shunt gap unit 5 inaccordance with the present invention, the unit is provided with endterminals 6 and 7 between which there are connected in series aplurality of main gaps, four being shown by way of example and beingdesignated G1, G2, G3 and G4 respectively, and also included serially inthe circuit is a magnetic coil 8 which is preferably physically andelectrically near the middle of the series circuit so that its magneticeld will have substantially equal strength between the electrodes of allof the gaps. A gap G5 generally similar to the other main gaps isconnected across the coil 8 for protecting it from overvoltages duringdischarge current operation of the arrester and for switching thedischarge current into the coil for increasing its magnetic eld andhence arc propelling action on the gaps G1 through G5. The gaps G1through G5 may be of any suitable physical construction and arepreferably of the familiar horn gap construction so that they inherentlytend to elongate their arcs, and the polarity of the coil S is made suchthat its magnetic field reinforces the individual magnetic fields of thegaps.

Also serially connected between the terminals 6 and 7 are auxiliary gapsS1, S2, S3 and S4 which not only act as preionizers for the respectivemain gaps G1, G2, G3 and G4 but also function to control the sequentialapplication of sparkover voltage to the main gaps. Thus auxiliary gap S1is mounted physically adjacent gap G1 so that when it sparks over itionizes or illuminates the space between the electrodes of G1 and thesame is true for S2 with respect to G2, S3 with respect to G3 and S4with respect to G4. Serially connected with the gaps S1 through S4 are apair of resistors R1 and R2, the former being provided for the purposeof impressing substantially all of the applied voltage across gap G1which, as will be explained hereinafter, is the lirst main gap to besparked over and which consequently can be called the trigger gap. Theresistor R2 is provided primarily for determining the level of appliedVoltage at which the trigger gap G1 sparks over. As shown, the resistorR1 is between S1 and S2 but this is not essential and the relativepositions of S1 and R1 can be reversed. However, it is important that R1in effect be ahead of S2, that is to say between S2 and terminal 6.Resistor R2 is connected between S2 and S3 for reasons which will becomeapparent hereinafter in explaining the operation of FIG. 2. A resistorR3 is connected across or in shunt with S1 and R1 and a resistor R4 isconnected across S4, these being provided for the purpose of producing adesired sequence of the sparkover of the gaps S1 to S4 inclusive.

Coupling resistors R5, R6 and R7 are provided for the purpose ofintermediate coupling of the circuit of the S gaps to the circuit of theG gaps, R5 being connected between the junction of G3-G4 and thejunction of S13-S4; R3 being connected between the junction of G3-G5 andthe junction of R2-S3, and R1 being connected between the junction ofG1-G2 and the junction of R1-S2. A capacitor C1 connected in shunt withR2 is provided for the purpose of making the sparkover voltage of thegap unit substantially independent of the wave shape of the appliedvoltage and a capacitor C2 connected in shunt with the coil 8 isprovided for the purpose of eilfectively short circuiting the coil untilafter gaps G1 through G4 have been caused to spark.

Th operation of FIG. 2 is as follows, it being assumed that G1 throughG5 have essentially the same electrode spacing and individual sparkovervoltage and the spark gaps S1 through S4 have an equal electrode spaceof somewhat less than half the spacing of the electrodes of the G gapsso that the S gaps each have asparkover voltage somewhat less than halfthe sparkover voltage of each of the G gaps. Assume now that the voltagebetween terminals 6 and 7 is increasing. In this connection it makes nodiilerence which is the higher voltage terminal but, for the purpose ofexplanation, it will be assumed that terminal 7 is the low voltageterminal which is maintained at ground potential and the terminal 6 isthe one whose potential is increasing relative to ground. It will alsobe assumed for the present that R2 and C1 are short circuited or that R2has substantially zero resistance which amounts to the same thing.Inasmuch as the eifective resistance of the gaps S2 and S3 is very muchhigher than the resistance of R3 and R4 practically all of the appliedvoltage will be across S2 and S3 so that when the applied voltageattains a value somewhat less than the sparkover voltage of a G gap S2and S3 will spark over. When S2 and S3 spark over, their arc voltage isvery much less than the voltage across R3 and R4 so that practically allof the applied voltage will then be across S1 and S4 and they will sparkover. At that time practically all of the applied voltage will be acrossR1, it being assumed for the time being that R2 has negligibleresistance. The sparked over gaps S1 through S4 now ionize theircorrespondingly numbered G gaps and when the applied voltage reaches avalue such that the voltage across R1 equals the sparkover voltage ofG1, G1 will spark over and its initial arc voltage will be low so thatinstantaneously the voltage on the upper electrode of G2 as viewed inthe drawing will be very close to the voltage of terminal 6 whereas thevoltage of the lower electrode of G2 will be very close to the voltageof terminal 7 because the right-hand terminal of coupling resistor 6 isat substantially the potential of terminal 7 because of the low arcdrops in S3 and S4 and consequently the lower electrode of G2, which istied to this point through R3 and C2 or coil 8 will also besubstantially at the same potential as terminal 7, Consequentlypractically all of the applied voltage will then be across G2 and itwill spark over. As the voltage across the capacitor C2 cannot changeinstantaneously, the voltage of the upper electrode of G3 willimmediately become substantially the voltage of the terminal 6 while thelower electrode of G3 remains substantially at the p0- tential ofterminal '7 to Which it is connected through sparked over gap S4 andcoupling resistor R5. Consequently substantially full applied voltagewill now be applied to G3 and it will spark over which in turn appliessubstantially full voltage across G4 whose upper electrode will then beat substantially the potential of terminal 6 and whose lower electrodeis connected to terminal G4 sparked over, practically the entire appliedvoltage will be across G and it will spark over thus completing thespark over of the entire gap unit 5 in a cascading manner at an appliedvoltage not much more than the sparkover voltage of the G `gapsindividually.

By using a finite resistor R3 `a smaller percentage of the total appliedVoltage will appear across R1 when all the S gaps have sparked over sothat the greater the resistance of R3 the greater the applied voltageneeded for sparking over the trigger gap G1. The value of R2 thusdetermines the sparkover setting of the gap unit 5. If R2 were equal inresistance to R1 then the voltage would be divided equally between G1and G3 (before either of them became sparked) and they both becometrigger gaps. With the arrangement shown in FIG. 2 then the maximumsparkover level of the gap unit cannot exceed twice that of anindividual G gap. If higher sparkover levels are desired they can beachieved by adding resistors in series with S3 above the junction withR5 and also in series Capacitor C1 functions to increase the currentthrough R1 as the rate of rise of applied voltage between terminals 6and 7 increases because capacitor current is proportional to rate ofchange of voltage applied across its terminals. Consequently the timelag effect of steep front applied voltages on the spark over of G1 iscompensated for by the fact that the extra capacitor current on steepfront applied voltages flows through R1 and thus increases the voltageapplied to the trigger gap G1.

An example of suitable numerical values for FIG. 2 is 44 mil sparkoverspacings of the G gaps giving a sparkover voltage of those gaps of about5.25 kv. The S gaps can have a spacing of about -20 mils with anaccompanying sparkover voltage of 2 or 3 kv. R1, R5 and R1 can have aresistance of about 10,000 ohms each, R2 can have :a resistance of about2200 ohms and R5, R5 and R1 can have a resistance of about 5600 ohmseach. C1 can have a capacitance of about 200 picofarads and C3 can havea capacitance of about 750 piocfarads. The above mentioned componentvalues result in `an overall gap unit sparkover voltage of about 7.7 kv.

Referring now to the modification shown in FIG. 3, gaps G1 through G5,coil 8 and preionizer gap S1 correspond respectively to the similarelements in FIG. 2. Resistor R1 corresponds generally to R1 in FIG. 2but the one in FIG. 3 ordinarily will have a very substantially higherohmic value. I1, I3 and I3 are simple corona type preionizers for maingaps G1, G3, G3 and G1 and are shown connected thereacross. ResistorsR2, R3 and R4 connected respectively across the corona perionizers I1,I2 and I3 together with R1 and the coil 8 form a series resistive typevoltage divider network which after S1 sparks over, as will be describedhereinafter, divides the total applied voltage in the desired ratioamongst the gaps G1 through G1. Capacitors C1 and C2 connectedrespectively across R3 and R4 provide a more favorable voltagedistribution among the main gaps for steeply rising applied voltagewaves so as to compensate the sparkover control circuit for thevolt-time lag characteristic ofthe main gaps. Capacitor C3 connectedacross coil 8 prevents any appreciable part of the applied voltage fromappearing across the coil and G5 until after gaps G1 through G1 havebeen sparked over as will be described hereinafter.

The operation of FIG. 3 is as follows. As the applied voltage rises, avalue will be reached at which gap S1 sparks over thereby providingionization for gap G1 and placing the total applied voltage across theresistance voltage divider network. R1 has a resistance many times thesum of the resistances of R3, R3 and R1 plus the resistance of coil 8.Consequently, most of the total applied voltage will then he across gapG1 and when the voltage across gap G1 reaches its sparkover v-oltage(typically about 5.25 kv.) G1 sparks over. Resistor R1 is noweffectively short circuited and a sharp rise in voltage appears acrossR2 through R1. Most of this voltage rise appears across R3,

however, because the voltage across capacitors C1 through C3 cannot bechanged instantaneously and R2 has a resistance many times the totalresistance of R3 plus R1. Consequently ionizer I1 suddenly providesionization for G3 which is now overvoltaged and it immediately sparks.In a like manner gap G3 is next to spark followed by G4 and finally G5.Thus the gaps G1 through G5 are forced to spark over in a cascadingmanner in an overall applied voltage only a little above the sparkoverlevel of any of the individual G gaps.

The capacitors serve a dual function. First, as already described, theyforce the cascading by forcing gaps G2 through G5 to be highlyovervoltaged one at a time after G1 has been sparked. Second, forsteeply rising applied waves, they modify the division of voltage in theresistor network (before G1 is sparked) in such a manner that G1 sees ahigher proportion of the applied voltage than it would for slowly risingwaves. This compensates for a time lag effect of gap G1 and makes thesparkover level ofthe overall gap assembly quite independent of appliedwaveshape down to very short times.

An example of suitable numerical resistance and capacitance values forthe circuit 0f FIG. 3 is as follows: R1 equals 68,000 ohms, R3 equals22,000- ohms, R3 equals 6,800 ohms and R4 equals 2,200 ohms; capacitorC1 equals picofarads, C3 equals 400 picofarads and C3 equals 1500picofarads.

It will be observed that the resistors vary in substantially geometricprogression having a common ratio of three and that the capacitors varyin a substantially geometric progression having a common ratio of four.The above mentioned component valuesresult in an overall gap unitsparkover voltage of about 7.7 kv.

In the FIG. 3 circuit having the above numerical resistance andcapacitance values S1 carries in the order of 75 milliamperes at thetime G1 sparks over. At this current level it acts as a very etiicientpreionizer and so the spark over of G1 is very stable. The remainingionizers I1 through I3 are called upon to operate on a very steepvoltage rise after G1 sparks and hence they also are very efficient. Asa result of the ethcient preionization and severe overvoltage of gaps G3through G5 the cascading sparkover action occurs with negligible timedelay. Spark over of this gap assembly occurs over a very narrow bandfor applied waves reaching sparkover level at any time from a few tenthsof a microsecond to several thousand microseconds. While FIG. 2 iscapable of achieving a lower sparkover level than FIG. 3 the latter hasthe advantage that it is simpler, uses fewer components and the powerdissipation in its resistors is less leading to possibly greaterreliability in service.

While there have been shown and described particular embodiments of theinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention, andtherefore it is intended by the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope ofthe invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A valve resistor shunting current switching gap unit for a lightningarrester comprising, in combination, at least two main spark gaps, amagnetic coil, said main gaps and coil being serially connected with thecoil in the middle, a spark gap connected across said coil, said sparkgaps all having about the same individual sparkover voltage, and meansfor sequentially sparking over said gaps at an applied voltage acrossthe series circuit which is between the individual sparkover voltage ofsaid gaps and the sum of the sparkover voltages of all said gaps, thesequence being such that one main gap sparks over before the coilshunting gap sparks over.

2. A unit as in claim 1 in which the sequence is such that one main gapsparks over first and the coil shunting gap sparks over last.

3. A gap as in claim 1 in which said means comprises an impedancenetwork connected to each of said gaps.

4. A gap as in claim 1 in which said means includes a capacitor formaking the value of said applied voltage at which the first gap sparksover substantially independent of the wave shape of said appliedvoltage.

5. A gap as in claim 1 in which said means includes individualpreionizers for said gaps.

6. A gap as in claim l in which said means comprises an impedancenetwork connected to each of said gaps and includes a capacitor formaking the value Iof said applied voltage at which the rst gaps sparkover substantially independent of the wave shape of said appliedvoltage, said means also including individual preionizers for said gaps.

7. An extra high voltage lightning arrester current switching shunt gapunit comprising, in combination, a pair of end terminals, four mainspark gaps G1, G2, G3 and Gg and a magnetic coil connected in serieswith the coil between G2 and G3 and with G1 and G1 connectedrespectively to said end terminals, a spark gap G5 connected across saidlcoil, said spark gaps all having substantially t'ne same sparkoverlever, and means comprising a network of a plurality of gradedresistance resistors con- "nected between said end terminals and topoints between `certain of said gaps including at least one preionizingspark gap S1 for main gap G1 connected in series with a highestresistance resistor across G1 and a capacitor connected across anotherresistor to force sparkover of the gaps G1 through G5 in a cascadingmanner in numerical order at a highly constant over-all applied voltageValue slightly exceeding their individual sparkover level and whichvoltage value is substantially independent of the wave shape of theapplied voltage.

8. A gap unit for a lightning arrester comprising, in combination, apair of end terminals, four main spark gaps G1, G2, G3, and G4respectively, a common magnetic arc propelling coil for said gaps, saidgaps being serially connected in numerical sequence between saidterminals with said coil connected serially therewith between G3 and G2,a spark gap G5 connected in shunt with said coil, all of said spark gapshaving substantially the same sparkover voltage level, a separatepreionizer spark gap S1, S2, S3 and S4 for each of the gaps G1, G2, G3and G4 respectively, said preionizer spark gaps all having a lowersparkover voltage level than said main spark gaps, all of saidpreionizer spark gaps being serially connected between said endterminals with a resistor R1 serially between S1 and S2 and a resistorR2 serially between S2 and S3, a resistor R3 connected in shunt with S1and R1, a resistor R4 connected in shunt with 5,1, a resistor R5connected between the junction of G3 and G4 and the junction of S3 andS4, a resistor R5 connected between the junction f G3 and the Icoil andthe junction of R2 and S3, a resistor R7 connected between the junctionof G1 and G2 and the junction of R1 and S2, a capacitor C1 connected inshunt with R2 fand the capacitor C2 connected in shunt with the coil,R1, R3 and R4 having substantially equal resistance, R5, R and R1 havingsubstantially equal resistance about half that of R1, R2 having aresistance about half that of R5, C2 Ihaving a capacitance about fourtimes that of C1.

9. A gap unit as in claim 8 in which said spark gaps G have a minimumelectrode spacing of about 44 mils and a sparkover voltage of about 5.25kv., said preionizer gaps have a minimum electrode spacing of about -20mils and a sparkover voltage of about 2 or 3 kv., R1 being about 10,000ohms, R2 being about 2,200 ohms, R5 being about 5,600 ohms, C1 beingabout 200 picofarads and C2 being about 750 picofarads.

10. In a lightning arrester current switching shunt gap unit of the typehaving an even number of similar main (horn) gaps, and a common arcelongating coil for said main gaps all connected in series (with saidcoil electrically and physically in the middle of said seriesconnection), and with another (horn) gap connected across said coil, allsaid gaps having substantially the same sparkover voltage, thecombination of an impedance network connected to said gap unit forlowering its over-all sparkover voltage, ilattening its volt-timesparkover characteristic (and raising its reseal voltage to preventrestrike when switching long duration sWitc-hing surge currents), saidnetwork comprising as many resistors as there are main gaps of differentresistance (in substantialiy a geometric progression having a commonratio of about three), a preionizing spark gap having a substantiallylower voltage sparkover than said main gaps mounted for ionizing one endof said main gaps, Said preionizing gap and the highest resistance oneof said resistors being serially connected across said end one of saidmain gaps, Said other resistors being respectively connected across theremaining main gaps in order of decreasing resistance with the nexthighest resistance resistor being connected across the main gap which isadjacent said end one of said main gaps, and with the lowest resistanceresistor being connected across the other end main gap, separate (coronatype) preionizers for respectively preionizing said remaining main gapsconnected respectively in parallel with the other resistors, and as manyas there are main gaps less one capacitors of different capacitance (insubstantially geometric progression having a common ratio of aboutfour), the highest capacitance capacitor being connected across saidcoil, the remaining capacitors being connected respectively across thelowest resistance resistors with the highest capacitance remainingcapacitor being connected across the lowest resistance resistor, andwith the next lower capacitance remaining capacitor being connectedacross the next highest resistance resistor.

1l. In an extra high voltage lightning arrester current switching shuntgap of the type having four main horn gaps and a common arc elongatingcoil for said main gaps all connected in series with said coilelectrically and physically in the middle of said seri-es connection andwith another horn gap connected across said coil, all of said gapshaving substantially the same electrode spacing, the combination of animpedance network -connected to said gap unit for lowering its overallsparkover voltage, flattening its volt-time sparkover voltagecharacteristic (and raising its reseal voltage to prevent restrike whenswitching long duration switching surge currents), said networkcomprising four resistors of diierent resistance (in substantially ageometric progression having a common ratio of about three), apreionizing spark gap having a substantially lower voltage spark overthan said main gaps mounted for ionizing the remaining end one of saidmain gaps, said preionizing gap and the highest resistance one of saidresistors being serially connected across said end one of said maingaps, said other resistors being repectively connected across theremaining main gaps in order of decreasing resistance with the nexthighest resistance resistor being connected across the main gap which isadjacent said end one of said main gaps, and with the lowest resistanceresistor being connected across the other end main gap, separate (coronatype) preionizers for respectively preionizing said remaining main gapsconnected respectively in parallel with the other resistors, and threecapacitors of different capacitance (in substantially geometricprogression having a common ratio of about four), the highestcapacitance capacitor being connected across said coil, the remainingcapacitors being connected respectively across t-he lowest resistanceresistors with the highest capacitance remaining capacitor bein-gconnected across the lowest resistance resistor, and with the next lowercapacitance remaining capacitor being connected across the next higherresistance resistor.

l2. In a lightning arrester, a gap unit comprising a pair of equalaccurately calibrated main gaps connected in series, a resistor, anauxiliary roughly calibrated spark gap having any sparkover voltagelower than the individual sparkover voltage of the main gaps, and meansincluding a common coupling element for effectively connecting theroughly calibrated Spark gap in shunt circuit relation with one main gapand the resistor in shunt circuit relation with the other main gap,whereby upon applying an increasing voltage to the gap unitsubstantially all of the applied voltage is .across the auxiliary sparkgap which consequently is rst sparked over at a value of applied voltageless than the sparkover voltage of a main gap so 'as then to limit thevoltage across said one main gap to the arc voltage of the auxiliaryspark gap thus causing substantially all of the applied voltage toappear across said other main gap which will next spark over when theapplied voltage attains that gaps accurately calibrated sparkovervoltage whereupon substantially all of the applied voltage istransferred to said one main gap for next sparking it over thusresulting in sequential cascaded sparkover of the serially connectedmain gaps at an applied voltage substantially equal to their individualsparkover voltage.

13. In a lightning arrester, a gap unit comprising a pair of equalaccurately vcalibrated main gaps connected in series, a resistor, anauxiliary roughly calibrated spark gap having any sparkover voltagelower than the individual sparkover voltage of the main gaps, and meansincluding a common coupling element for effectively connecting theroughly calibrated spark gap in shunt circuit relation with one main gapand the resistor in shunt circuit relation with the other main gap,whereby upon applying an increasing voltage to the gap unit theauxiliary spark gap is rst sparked over a value of applied voltage lessthan the sparkover voltage of a main gap so as to limit the voltageacross said one main gap to the arc voltage of the auxiliary spark gapthus causing substantially all of the applied voltage to appear acrosssaid other main gap which will next spark over when the applied voltageattains that gaps accurately calibrated sparkover voltage whereuponsubstantially all of the applied voltage is trans ferred to Said onemain gap for next sparking it over resulting in sequential cascadedsparkover `of the serially connected main gaps at an applied voltagesubstantially equal to their individual sparkover voltage.

14. In a lightning arrester, a gap unit comprising a pair of equalaccurately calibrated main gaps connected in series, a resistor, anauxiliary roughly calibrated spark gap, and means including a commoncoupling resistor for elfectively connecting the resistor in shuntcircuit relation with one main gap and the roughly calibrate-d spark gapin shunt circuit relation with the other main gap, said auxiliary sparkgap having a lower sparkover voltage than the individual sparkovervoltage of the main gaps whereby upon applying an increasing voltage tothe gap unit the auxiliary spark gap first sparks over so as t0 limitthe voltage across its shunt connected main gap to the arc voltage 0fthe auxiliary spark gap thus causing substantially all of the appliedvoltage to appear across the remaining gap which will then spark overwhen the applied voltage reaches that gaps accurately calibratedsparkover voltage whereupon substantially all of the applied voltage istransferred to the remaining main gap for sparking it over resulting insequential cascaded sparkover of the series connected main gaps at anapplied voltage substantially equal to their individual sparkovervoltage.

15. In a lightning arrester, a gap unit comprising a pair of similaraccurately calibrated main gaps in series, a resistor in shunt with onemain gap, an auxiliary roughly calibrated spark gap in shunt wit-h theother main gap, and a coupling resistor connected between the junctionof the main gaps and the junction of the resistor and the auxiliaryspark gap, said auxiliary spark gap having a lower sparkover voltagethan the sparkover voltage of the main gaps, whereby upon applying anincreasing voltage to t-he gap unit the auxiliary gap rst sparks over soas to limit the voltage across the main gap which is shunted by theauxiliary gap to the arc volta-ge of the auxiliary gap thus causingsubstantially all the applied voltage to appearY across the remainingmain gap which will then spark over when the applied voltage reaches theaccurately calibrated sparkover voltage of said main gap whereuponsubstantially all the applied voltage is transferred to the remainingmain gap for sparking it over resulting in sequential cascaded sparkoverof the series connected main gaps at an applied voltage equal to thesparkover voltage of one of them.

References Cited UNITED STATES PATENTS 730,601 6/1903 Ben -317-703,259,792 7/19661 Jensen 315-36 FOREIGN PATENTS 1,268,953 6/1961 France.

MILTON O. HIRSHFIELD, Primary Examiner.

J. D. TRAMMELL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,348,100 October 17, 1967 James S. Kresge It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 2, line Z3, for "seen" read seem line 45, for "preioning" readpreionizing column 4, line 74, after "terminal" insert 7 so that itsparks over. Finally with gaps Gl through column 5, line 38, for"pocfarads" read picofarads line 6l, after "Coil" insert 8 column 8,line 13, after "end" insert one Column 9, line 30, after "over" insertat Signed and sealed this 26th day of November 1968.

(SEAL) Attest:

EDUHU)J.BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. A VALVE RESISTOR SHUNTING CURRENT SWITCHING GAP UNIT FOR A LIGHTNINGARRESTER COMPRISING, IN COMBINATION, AT LEAST TWO MAIN SPARK GAPS, AMAGNETIC COIL, SAID MAIN GAPS AND COIL BEING SERIALLY CONNECTED WITH THECOIL IN THE MIDDLE, A SPARK GAP CONNECTED ACROSS SAID COIL, SAID SPARKGAPS ALL HAVING ABOUT THE SAME INDIVIDUAL SPARKOVER VOLTAGE, AND MEANSFOR SEQUENTIALLY SPARKING OVER SAID GAPS AT AN APPLIED VOLTAGE ACROSSTHE SERIES CIRCUIT WHICH IS BETWEEN THE INDIVIDUAL SPARKOVER VOLTAGE OFSAID GAPS AND THE SUM OF THE SPARKOVER VOLTAGE OF ALL SAID GAPS, THESEQUENCE BEING SUCH THAT ONE MAIN GAP SPARKS OVER BEFORE THE COILSHUNTING GAP SPARKS OVER.